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January 15, 2007

Going the Metric Mile: After Loss of Mars Orbiter, NASA Ready to Use Decimal Unit System for Lunar-Base Surface Operations

by Sam Savage

By A.J. Hostetler

Don't bother asking for a two-by-four from astronauts building the first lunar base. And don't go racing your moon buggy across the Sea of Tranquility at 65 mph.

Still smarting from the metric-English mix-up that caused a Mars orbiter to disappear, NASA's ready to go all-metric on the moon.

The move will apply only to surface operations for the lunar base NASA wants to build. That means measurements for the robotic rovers, the nuts and bolts on the habitat modules and the distances for future golf shots will be in the system preferred by scientists, if not Americans.

The new spacecraft under development to get the astronauts to the moon by 2020, however, will continue to mix metric and English units.

NASA's decision came after meetings with 13 space agencies in Russia, Europe, Canada and Asia -- potential partners for the agency's lunar ambitions.

The move will standardize equipment and parts, paving the way for metric-based countries to contribute to the lunar project, said Geoff Yoder, leader of NASA's lunar architecture team. That means every country but Burma and Liberia.

"Going metric will show our potential partners that we are serious," Yoder said. "It ultimately will help reduce risk as we interface across the different agencies."

Using metric will help, for example, in satellite communications that tell astronauts how many kilometers to drive the lunar rovers. Metric-minded astronauts will avoid the embarassing hassle of trying to fit a 15-millimeter nut onto a 5/8-inch bolt on the habitat modules.

Sharing equipment with international partners such as Europe and Japan could help cut the cost of shipping and handling to the moon. Why buy that new set of wrenches and ship it 238,855 miles -- whoops, that's 384,400 km -- into space when you can "borrow" it from your neighbors?

Going metric will also help ensure quality and safety as NASA returns to the moon and plans to head to Mars, said Russell Lefevre, president-elect of the engineering organization IEEE-USA.

Metric, also known as the International System of Units or SI, is the preferred system in science, engineering and technology.

Aerospace engineer James Marchman, who teaches international aircraft design at Virginia Tech, said NASA's move was common sensical.

Mixing units "creates both confusion and a need for duplication," Marchman said. "If everyone is using the same unit system there should be fewer mistakes made."

NASA would prefer not to miss Mars again.

The space agency's 1999 mishap with its $125 million Mars Climate Orbiter subjected the agency to countless late-night TV jokes. The orbiter careened off course because contractor Lockheed Martin failed to convert thruster-firing data from English units to metric. No one noticed until it was too late.

Two years later, an internal report rebuked the agency for failing to follow its own pro-metric policy. Still, for the next three years, NASA refrained from implementing all the report's recommendations aimed at avoiding another catastrophic mix-up between measuring systems.

Instead, NASA continued to grant exemptions to allow programs to use the English system. NASA mixes metric and English systems for the space shuttles, the International Space Station and robotic missions.

NASA's reasons for not converting include its long-standing complaint about the difficulty in purchasing metric parts from the U.S. aerospace industry, one of the remaining large industries in the country that has held out against metric.

Rep. Vernon J. Ehlers, R-Mich., who has pushed legislation to force NASA contractors' conversion to metric, was delighted with the decision.

"It's totally absurd for the most advanced nation in the world to be out of step with other nations . . . and to in fact hamper our efforts to do business with the rest of the world because we don't use the metric system as extensively as we should," Ehlers said.